Sound reproduction apparatus



Dec. 30, 1952 A. J; CORKE SOUND REPRODUCTION APPARATUS Filed March 6,1951 JNVENTOR. W; C fl I M Patented Dec. 30, 1952 UNITED STATES PATENTOFFICE Application March 6, 1951, Serial No. 214,040 In Great BritainJune 30, 1948 8 Claims.

This invention which is a continuation in part of my application SerialNo. 98,837, filed June 13, 1949, concerns sound propagation from sourcessuch as loudspeakers.

It is an object of the invention to provide a sound reproduction unitwhich has a pleasing appearance and possesses good acoustic properties.

It .is a further object of the invention to provide a sound reproductioncabinet which does not reveal, by its external appearance, that anysound reproduction means are contained therein.

According to the present invention an electroacoustic apparatus includesfour upstanding elements comprising two sides, a back and a front, a topfor said apparatus, said top together with said four upstanding elementsenclosing said apparatus at the top, the back and the two sides, saidfront extending downwardly and defining with a lower edge thereof, theupper limit of a transverse aperture, a mounting plate upwardly andforwardly inclined inside the four upstanding elements dividing thespace defined by said four elements into an upper compartment, and alower compartment of substantially constant transverse dimension, 9.sound reproduction device mounted on said mounting plate orientated toemit sound mainly in a downwardly and forwardly inclined direction intosaid lower cornpartment, and a downwardly and forwardly inclinedreflecting board forming the base of said lower compartment, whichcompartment is adapted to serve as a resonance chamber, said frontextending downwardly past the forward edge of said mounting plate to alower level than any part of said sound reproduction device, saidaperture thereby serving as a restricted outlet from said lowercompartment.

According to a further feature of the invention a substantially verticaltie connects said mounting plate and said reflecting board.

The invention will be described further by way of example with referenceto the accompanying drawings in which:

Fig. 1 is a general perspective view of a sound reproduction cabinet inaccordance with the in vention,

Fig. 2 is a transverse vertical section of the cabinet shown in Fig. 1,and

Fig. 3 is an inverted plan view corresponding to Fig. 2.

The cabinet includes two end faces II, a front face l2 and a back IS.The front face l2 terminates above the level of the lower edges of endfaces II, thus providing an aperture 12a at the base of the cabinet. Amounting plate [4 is disposed within the cabinet and carries centrallythereon a loudspeaker IS. The position of the mounting plate is suchthat the loudspeaker cannot be seen when the cabinet is viewed from thefront at other than very oblique angles. The mounting plate I4 isinclined downwardly from the front of the cabinet to the back, so thatthe axis of the loudspeaker I5 is downwardly inclined from the back ofthe cabinet to the front. Mounting plate 14 may have a number of holes Ila drilled therein.

A number of louvres I6 are situated in the back l3 of the cabinet, theselouvres being rotatable about horizontal axes. Variation in the settingof the louvres varies resonating properties of the cabinet to someextent and such variation thus constitutes a mechanical means of tonecontrol.

The back [3 also has a number of ventilation holes therein.

At the base of the cabinet is a sound reflecting board 11. This soundreflecting board slopes downwardly from the back of the cabinet to thefront, preferably at an angle of about 20 to the horizontal.

The angle of the mounting plate Hi to the horizontal may be betweenabout 15 and about 50. Preferably this angle is about 30.

Air should have free access to the space beneath the sound reflectingboard I! and for this purpose the back I 3 of the cabinet terminatesabove the base level of the apparatus, or an architrail may be providedwith air holes or slots therein. This is necessary since the board I! awell as reflecting sound is designed to resonate in sympathy withimpinging sound waves.

Between the mounting plate M and the sound reflecting board I? a tiecomprising a metal bar iii and acoaxial tube 19 of suitable materialsuch as wood or synthetic resin, is provided. The ends of the metal bar[8 pass through the mounting plate l4 and the reflecting board I!respectively and thereafter are accommodated in clearance holes inblocks 20 secured to the outer surfaces of board and plate. The uppersurface of the block 20 secured to the mounting plate [4 and the lowersurface of the block 20 secured to the reflecting board I! are flat,parallel and at right angles to the metal bar H3. The ends of the metalbar l8, which are threaded, extend beyond these block surfaces andreceive wing nuts 2! for tightening purposes. The coaxial tube [9extends only between the board I! and the plate It and its ends aresuitably chamfered to provide good contact therewith.

Along the underside of the reflecting board I! is glued and/or screwed anarrow strip 22 of material suitable for weighting and reinforcing theboard l1. It extends substantially transversely of the cabinet for themaior part of the width of the sound reflecting board ll. It has beenfound advantageous to have the strip 22 of material either close to oron the transverse centre line of the reflecting board I1 and also tohave the tie disposed substantially centrally of the board length andnear to the speaker aperture.

The tie will of course have to be offset transversely of tie board I 1because of the loud-speaker aperture.

Seatings 23 of sorbo rubber have been found suitable for supporting atleast the mounting board M, which may be conveniently angularlyadjustable. The sound reflecting board I! has been found satisfactorywhen it has a hard smooth surface given, for example, by a hard woodveneer and a satisfactory thickness for many types of loud speaker usedfor domestic purposes has been found to be approximately ,4 The mountinplate should be about four times this thickness.

For uses such as public sound reproduction e. g. in cinemas the ratio4:1 of the thickness of the mounting plate reflecting board should bemaintained, the actual dimensions increasing, for instance, toapproximately 1" and A" respectively.

The improvements and modifications which are the subject of the presentinvention have been found extremely beneficial to the quality of thereproduced sound. The tie prevents the sound reflecting board I? and themounting plate M, which both tend to vibrate, when the apparatus is inuse, doing so out of phase, and prevents any consequent woolly acousticeffect. The wing nuts enable the tie to be adjusted within small limitsand a suitable condition can be found under most circumstances by trialand error. The extra strip of material added to the underside of thesound reflectin board also improves the quality of sound emitted fromthe cabinet and in particular aids in the reproduction of :a pure baseresponse.

In some circumstances it may be found necessary to adjust the anglebetween the board and the plate and it is for this purpose that themounting plate may be made adjustable.

I claim:

1. An electro-acoustic apparatus including four upstanding elementscomprising two sides, a back and a front, a top for said apparatus, saidtop together with said four u standing elements enclosing said apparatusat the top, the back and the two sides, said front extendin downwardlyfrom the top of said apparatus and being cut away in its lower region toform a transverse aperture, the upper and side edges of which aredefined by the lower edge of said front and by the two sides of saidapparatus respectively, a plane mounting plate upwardly and forwardlyinclined inside the four upstanding elements dividing the space definedby said four elements into an upper compartment, and a lower compartmentof substantially constant transverse dimension, 9, sound reproductiondevice mounted on said plane mounting plate within said uppercompartment orientated to emit sound mainly in a downwardly andforwardly inclined direction into said lower compartment, and adownwardly and forwardly inclined plane reflecting board forming thebase of said lower compartment and so disposed within said apparatus asto meet the back thereof at the same place as said mounting plate 4 sothat the lower compartment comprises a resonance chamber ofsubstantially constant width across said apparatus and of generallytriangular cross section, with said transverse aperture disposed in thatside of the triangle pre sented by the front of the apparatus, saidresonance chamber serving to increase the reverberation time within saidapparatus of sound waves emitted by said reproduction device, said frontextending downwardly past the forward edge of said plane mounting plateto a level lower than any part of said sound reproduction device wherebythe resonating properties of said lower compartment are improved andsaid transverse aperture serves as a restricted outlet from said lowercompartment.

'2. An electro-acoustic apparatus including four upstanding elementscomprising two sides, a back and a front, a top for said apparatus, saidtop together with said four upstanding elements enclosing said apparatusat the top, the back and the two sides, said front extending downwardlyfrom the top of said apparatus and being cut away in its lower region toform a transverse aperture, the upper and side edges of which aredefined by the lower edge of said front and by the two sides of saidapparatus respectively, said back having at least one aperture therein,upwardly and backwardly inclined louvre means for closing said aperture,pivotal means rotatably mounting said louvre means in said back wherebysaid aperture is adjustable in size, a plane mounting plate upwardly andforwardly inclined inside the four upstanding elements dividing thespace defined by said four elements into an upper compartment, and alower compartment of substantially constant transverse dimension, asound reproduction device mounted on said plane mounting plate withinsaid upper compartment and orientated to emit sound mainly in adownwardly and forwardly inclined direction into said lower compartmentto emerge from said transverse aperture, and a downwardly and forwardlyinclined plane refleeting board meeting the back of the apparatus at thesame place as said plane mounting plate and forming the base of saidlower compartment.

which is adapted to serve as a resonance chamber to increase thereverberation time within said apparatus of sound waves emitted by saidreproduction device, said front extending down-v wardly past the forwardedge of said plane mounting plate to a level lower than any part of saidreproduction device, whereby the resonating properties of said lowercompartment are improved and said transverse aperture serves as arestricted outlet from said lower compartment, said louvre means beingdisposed at the rear of said up er compartment to form a variable soundoutlet therefrom.

3. An electro-acoustic apparatus including four upstanding elementscomprising two sides, a back and a front. a top for said apparatus, saidtop together with said four upstanding elements enclosing said apparatusat the top, the. back and the two sides, said front extending.

downwardly from the top of said apparatus and being cut away in itslower region to form a transverse aperture, the upper and side edges ofwhich are defined by the lower edge of said front and by the two sidesof said apparatus respectively, a plane mounting plate upwardly andforwardly inclined inside the four upstanding elements dividing thespace defined by said four elements into an upper compartment, and alower compartment of substantially constant transverse dimension, asound reproduction device mounted on said plane mounting plate withinsaid upper compartment orientated to emit sound mainly in a downwardlyand forwardly inclined direction into said lower compartment, adownwardly and forwardly inclined plane reflecting board forming thebase of said lower compartment and so disposed within said apparatus asto meet the back thereof at the same place as said mounting plate, sothat the lower compartment comprises a resonance chamber ofsubstantially constant widthacross said apparatus and of generallytriangular cross section, with said transverse aperture disposed in thatside of the triangle presented by the front of the apparatus, and asubstantially vertical tie connecting said mounting plate and saidreflecting board, said resonance chamber serving to increase thereverberation time within said apparatus of sound waves emitted by saidreproduction device, saidfront extending downwardly past the forwardedge of said plane mounting plate to a level lower than any part of saidsound reproduction device whereby the resonating properties of saidlower compartment are improved and said transverse aperture serves as arestricted outlet from said lower compartment 4. An electro-acousticapparatus as set forth in claim 3 including a long narrow strip ofmaterial fixed, substantially transversely of the apparatus, to theunderside of said reflecting board to act as a reinforcement andweighting therefor.

5. An electro-acoustic apparatus including four upstanding elementscomprising two sides, a back and a front, a top for said apparatus, saidtop together with said four upstanding elements enclosing said apparatusat the top, the back and the two sides, said front extending downwardlyfrom the top of said apparatus and being cut away in its lower region toform a transverse aperture, the upper and side edges of which aredefined by the lower edge of said front and by the two sides of saidapparatus respectively, said back having at least one aperture therein,upwardly and backwardly inclined louvr means for closing said aperture,pivotal means rotatably mounting said louvre means in said back wherebysaid aperture is adjustable in size, a plane mounting plate upwardly andforwardly inclined inside the four upstanding elements dividing thespace defined by said four elements into an upper compartment, and alower compartment of substantially constant transverse dimension, asound reproduction device mounted on said plane mounting plate withinsaid upper compartment and orientated to emit sound mainly in adownwardly and forwardly inclined direction into said lower compartmentto emerge from said transverse aperture, and a downwardly and forwardlyinclined plane reflecting board meeting the back of the apparatus at thesame place as said plane mounting plate, so that the lower ocmpartmentcomprises a resonance chamber of substantially constant width acrosssaid apparatus and of generally triangular cross-section, with saidtransverse aperture disposed in that side of the triangle presented bythe front of the apparatus, a substantially vertical tie connecting saidmounting plate and said reflecting board, and a long narrow strip ofmaterial, fixed substantially transversely of the apparatus to theunderside of said reflecting board to act as a reinforcement andweighting therefor, said resonance chamber 6 serving to increase thereverberation time within said apparatus of sound waves emitted by saidreproduction device, said front extending downwardly past the forwardedge of said plane mounting plate to a level lower than any part of saidsound reproduction device whereby the resonatin properties of said lowercompartment are improved and said transverse aperture serves as arestricted outlet from said lower compartment.

6. An electro-acoustic apparatus including four upstanding elementscomprising two sides, a back and a front, a top for said apparatus, saidtop together with said .four upstanding elements enclosing saidapparatus at the top, the back and the two sides, said front extendingdownwardly from the top of said apparatus and being cut away in itslower region to form a transverse aperture, the upper and side edges ofwhich are defined by the lower edge of said front and by the two sidesof said apparatus respectively, said back having at least one aperturetherein, upwardly and backwardly inclined louvre means for closing saidaperture, pivotal means rotatably mountin said louvre means in said backwhereby said aperture is adjustable in size, a plane mounting plateupwardly and forwardly inclined inside the four upstanding elementsdividing the space defined by said four elements into an uppercompartment, and a lower compartment of substantially constanttransverse dimension, a sound reproduction device mounted on said planemounting plate within said upper compartment and orientated to emitsound mainly in a downwardly and forwardly inclined direction into saidlower compartment to emerge from said transverse aperture, and adownwardly and forwardly inclined plane reflecting board meeting theback of the apparatus at the same place as said plane mounting plate sothat the lower compartment comprises a resonance chamber ofsubstantially constant width across said apparatus and of generallytriangular cross-section, with said transverse aperture disposed in thatside of the triangle presented by the front of the apparatus, asubstantially vertical tie connecting said mounting plate, and saidreflecting board, said tie consisting of a bar which passes at its endsthrough the mounting plate and the reflecting board respectively, meansbeyond said mounting plate and said reflecting board respectively tosecure said bar in position, a tube disposed coaxially on that part ofsaid bar lying between the mounting plate and the reflecting board, anda long narrow strip of material, fixed substantially transversely of thapparatus to the underside of said reflecting board to act as areinforcement and weighting therefor, said resonance chamber serving toincrease the reverberation time within said apparatus of sound Wavesemitted by said reproduction device, said front extending downwardlypast the forward edge of said plane mounting plate to a level lower thanany part of said sound reproduction device whereby the resonatingproperties of said lower compartment are improved and said transverseaperture serves as a restricted outlet from said lower compartment.

7. An electro-acoustic apparatus as set forth in claim 6 in which theends of said bar are threaded, and including blocks attached to saidmounting plate and said reflecting board through which the threaded endsof said bar are adapted to pass, and wing nuts to fit the threaded endsof said bar to adjust and secure said b in position.

8. An electro-acoustic apparatus including four upstanding elementscomprising two sides, a back and a front, a top for said apparatus, saidtop together with said four upstanding elements enclosing said apparatusat the top, the back and the two sides, said front extending downwardlyfrom the top 01" said apparatus and bein cut away in its lower region toform a transverse aperture, the upper and side edges of which aredefined by the lower edge of said front and by the two sides of saidapparatus respectively, a resiliently secured plane mounting plateupwardly and forwardly inclined inside the four upstanding elementsdividing the space defined by said four elements into an uppercompartment, and a lower compartment of substantially constanttransverse dimension, a sound reproduction device mounted on said planemounting plate within said upper compartment orientated to emit soundmainly in a downwardly and forwardly inclined direction into said lowercompartment, a downwardly and forwardly inclined reflecting board havinga hard and smooth surface, and forming the base of said lowercompartment, which reflecting board is so disposed within said apparatusas to meet the back thereof at the same place as said mounting plate, sothat the lower compartment comprises a resonance chamber ofsubstantially constant width across said apparatus and of generallytriangularcro'ss-section, with said transverse aperture disposed in thatside of the triangle presented by the front of the apparatus, asubstantially vertical tie connecting said mounting plate and saidr'efiecting'board, said tie consisting of a bar which passes at itsends, through the mounting plate 8 and the reflecting boardrespectively, means beyond said mounting plate and said reflecting boardrespectively to secure said bar in position, a tube disposed coaxiallyon that part of said bar lying between the mounting plate and thereflecting board, and a long narrow strip of material, fixedsubstantially transversely of the apparatus to the underside of saidreflecting board to act as a reinforcement and weighting therefor, saidresonance chamber serving to increase the reverberation time within saidapparatus of sound Waves emitted by said reproduction device, said frontextending downwardly past the forward edge of said plane mounting plateto a level lower than any part of said sound reproduction device wherebythe resonatin properties of said lower compartment are improved and saidtransverse aperture serves as a restricted outlet from said lowercompartment.

ALFRED JAMES CORKE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,830,812 Schloss et al Nov. 10,1931 1,887,629 Forse et a1 Nov. 15, 1932 1,932,343 Holland Oct. 24, 19332,034,014 Wheeler et a1 Mar. 17, 1936 2,205,804 Wells June 25, 19402,373,692 Klipsch Apr. 17, 19fl5 2,ll0,078 Devine Apr. 20, 19482,511,917 Hornor June 20, 1950

